In treating contaminated water, such as waste water or the like resulting from agricultural or industrial processes, it is necessary to mix treatment additives with the contaminated water in order to effectively remove the contaminants. For example, in flotation systems wherein the contaminants are removed through the process of coalescing bubbles which float to the surface and form flocs which can be skimmed or otherwise removed from the liquid, additives such as cationic substances, anionic substances, acids, bases, clay, diatomaceous, earth, coagulants and polymers are used to selectively alter the contaminated liquid chemistry and remove the contaminants.
It is preferred that the contaminated liquid and treatment additives form a homogenous mixture such that when the dissolved gas is added and subsequently allowed to coalesce into bubbles, a good majority of the contaminants will be taken to the surface with the bubbles. If the mixture is not homogenous, an unacceptable amount of contaminants may remain in the liquid even after treatment.
In the past, treatment additives have been added to the contaminated liquid in several manners. For example, treatment additives are often mixed into a tank of contaminated liquid and then mechanically stirred with a mixer or the like. However, it has been found that the treatment additives tend to xe2x80x9cglobxe2x80x9d to each other prematurely.
As shown in FIG. 1, treatment additives having a monomer backbone and a positive charge site can cluster or xe2x80x9cglobxe2x80x9d, preventing all of the negatively charged waste particles from being attached thereto, resulting in incomplete mixing and excessive use of treatment chemistry. After adding coagulant 16, polymers and anionic or cationic polymers 10 and 12 are often added to the contaminated liquid in order to cluster the strands of polymers to one another to create clusters of sufficient size so as to be removed in the flotation and flocculation process. However, due to the fact that the polymer strands are wound or xe2x80x9cglobbedxe2x80x9d together, the polymer 16 can only attach a minimal amount of waste particles 14 to the polymers 10 and 12. Thus, free-floating waste particles 14 and coagulants 16 may not be removed due to their size, or the treatment process of removing such contaminants which relies upon the attachment of the waste particle 14 to the polymers 10 and 12. Additionally, an excess amount of coagulant 16 will probably be introduced into the contaminated liquid in an attempt to coagulate to the greatest extent possible, thus wasting valuable coagulant and polymer.
Thus, such mixing is imprecise and optimal mixing is not achieved. This can result in wasting valuable chemical treatment additives, and also result in the failure of removing as many contaminants as possible.
Others have added chemicals and other treatment additives into a flowing contaminated stream. This stream has been introduced into a mixing device, typically a hydrocyclone. However, the inventors have found that certain treatment additives are very sensitive to the speed of the flowing liquid. Thus, over mixing, as well as under mixing, can have deleterious effects on the additives and may alter their behavior or efficiency. The inventors of the present invention have also found that the mixing time for various treatment additives vary according to the speed of the fluid. However, over mixing, once again, can have deleterious effects on certain treatment additives. In the past, it was believed that vigorous mixing over a prolonged period of time provided optimal mixing. However, the inventors have found that this is not the case.
Accordingly, there is a need for a method of mixing treatment additives to contaminated liquid which optimizes the time and speed of mixing to homogeneously mix and efficiently utilizes the treatment additives, thus requiring less additives and facilitating optimum removal of the contaminants from the liquid. The present invention fulfills these needs and provides other related advantages.
The present invention resides in a process for mixing treatment additives to contaminated liquid, such as waste water, so as to optimize the mixing between the contaminated liquid and the treatment additives, and in order to utilize the lowest amount possible of the treatment additive. First, one or more treatment additives are selected. This includes the step of determining the identity of the additives and the amount of each additive needed to treat the contaminated liquid. This entails mixing various treatment additives to a sample of the contaminated liquid over time and determining the effective additives, and the amount of each additive necessary to treat a given volume of contaminated liquid.
Next, a mixing energy requirement of the contaminated liquid and the selected treatment additives is determined. The mixing energy requirement is determined by mixing the treatment additives over a range of mixing time and mixing speeds, and measuring turbidity to determine the mixing time and speed which results in the lowest turbidity. For example, a low mixing energy requirement requires a lower mixing time and mixing speed than a higher mixing energy requirement. Typically, for convenience, the mixing energy requirement is classified into either a low mixing energy requirement corresponding to lower mixing speeds and time, a medium mixing energy requirement based on higher mixing speeds and time, and a high mixing energy requirement based upon yet higher mixing speeds and time.
The contaminated liquid and the selected treatment additives are then directed into a mixing system. The mixing system includes at least one hydrocyclone having an inlet aspect ratio selected based upon the mixing energy requirement determination. The barrel length and diameter of the hydrocyclone are also selected based upon the mixing energy requirement determination. The aspect ratio of the hydrocyclone comprises the cross-sectional area of the inlet. Thus, the inlet is enlarged to correspond with a lower mixing energy requirement, and reduced in cross-sectional area to correspond to a higher mixing energy requirement. This is due to the fact that a smaller inlet will result in a higher velocity or speed of the liquid, whereas a larger cross-sectional area inlet results in a slower stream speed through the hydrocyclone. By increasing the diameter or the length of the hydrocyclone barrel, the overall mixing time is increased. Similarly, decreasing the length of the hydrocyclone barrel decreases the mixing time. Altering the diameter of the barrel can also effect the speed of the mixing.
In a particularly preferred embodiment, a plurality of hydrocyclones are fluidly coupled with one another. This can enable an appropriate mixing time throughout the length of the coupled hydrocyclones. Also, this enables the adding of treatment additives in stages throughout the mixing system. The aspect ratio and barrel length/diameter of each hydrocyclone can be selected based upon the mixing energy requirement determination of each treatment additive or group of treatment additives added to the contaminated liquid immediately upstream from that hydrocyclone.
The result of the mixing method of the present invention is a homogenous mixture which has been completely mixed and which has optimized the amount of treatment additives.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.